1. Microprocessor Interface
Op-Amps
Microprocessor Interface

2. Operational Amplifier (Op-Amp)
Very high differential gain
High input impedance
Low output impedance
Provide voltage changes (amplitude and polarity)
Used in oscillator, filter and instrumentation
Accumulate a very high gain by multiple stages

3. IC Product
DIP-741
Dual op-amp 1458 device

4. Distortion
The output voltage never excess the DC voltage supply of the Op-Amp

5. Op-Amp Properties Infinite Open Loop gain (2) Infinite Input impedance
The gain without feedback
Equal to differential gain
Zero common-mode gain
Pratically, Gd = 20,000 to 200,000
(2) Infinite Input impedance
Input current ii ~0A
T- in high-grade op-amp
m-A input current in low-grade op-amp
(3) Zero Output Impedance
act as perfect internal voltage source
No internal resistance
Output impedance in series with load
Reducing output voltage to the load
Practically, Rout ~ 

6. Frequency-Gain Relation
Ideally, signals are amplified from DC to the highest AC frequency
Practically, bandwidth is limited
741 family op-amp have an limit bandwidth of few KHz.
20log(0.707)=3dB
Unity Gain frequency f1: the gain at unity
Cutoff frequency fc: the gain drop by 3dB from dc gain Gd
GB Product : f1 = Gd fc

7. GainBandwidth Product
Example: Determine the cutoff frequency of an op-amp having a unit gain frequency f1 = 10 MHz and voltage differential gain Gd = 20V/mV
Sol:
Since f1 = 10 MHz
By using GB production equation
f1 = Gd fc
fc = f1 / Gd = 10 MHz / 20 V/mV
= 10  106 / 20  103
= 500 Hz
10MHz
? Hz

8. Ideal Op-Amp Applications
Analysis Method :
Two ideal Op-Amp Properties:
The voltage between V+ and V is zero V+ = V
The current into both V+ and V termainals is zero
For ideal Op-Amp circuit:
Write the kirchhoff node equation at the noninverting terminal V+
Write the kirchhoff node eqaution at the inverting terminal V
Set V+ = V and solve for the desired closed-loop gain

9. Noninverting Amplifier
Kirchhoff node equation at V+ yields,
Kirchhoff node equation at V yields,
Setting V+ = V– yields or

10. Noninverting amplifier
Noninverting input with voltage divider
Less than unity gain
Voltage follower

11. Inverting Amplifier Kirchhoff node equation at V+ yields,
Setting V+ = V– yields
Notice: The closed-loop gain Vo/Vin is dependent upon the ratio of two resistors, and is independent of the open-loop gain. This is caused by the use of feedback output voltage to subtract from the input voltage.

12. Multiple Inputs Kirchhoff node equation at V+ yields,
Setting V+ = V– yields

13. Inverting Integrator
Now replace resistors Ra and Rf by complex components Za and Zf, respectively, therefore
Supposing
The feedback component is a capacitor C, i.e.,
The input component is a resistor R, Za = R
Therefore, the closed-loop gain (Vo/Vin) become:
where
What happens if Za = 1/jC whereas, Zf = R
Inverting differentiator

14. Op-Amp Integrator Example: Determine the rate of change
of the output voltage.
Draw the output waveform.
Solution:
(a) Rate of change of the output voltage
(b) In 100 s, the voltage decrease

15. Op-Amp Differentiator

16. Slew Rate
The maximum possible rate at which an amplifier’s output voltage can change, in volts per second, is called its slew rate.
FIGURE The rate of change of a linear, or ramp, signal is the change in voltage divided by the change in time